Triplate transition jointsTriplate transition joints

The ultimate solution to weld The ultimate solution to weld aluminium to steelaluminium to steel

By Ko Buijs

Metallurgical engineer SMT-Metals b.v.

Vacuum cladding

Production route of TriplateProduction route of Triplate

• Choice of right materials and study of featuresChoice of right materials and study of features• Grinding of the surfacesGrinding of the surfaces• Preparing of special grade explosivesPreparing of special grade explosives• Preparing vacuum chamberPreparing vacuum chamber• Explosion weldingExplosion welding• Flattening of the platesFlattening of the plates• Cutting into bars and special shapesCutting into bars and special shapes• Inspection by QA-manager and independent Inspection by QA-manager and independent

surveyorsurveyor• Transport to customerTransport to customer• After sales and all kind of recommendations After sales and all kind of recommendations

What happens during What happens during weldingwelding??

Steel plate

Aluminium plate

Explosives

S = collision point high pressure will locally cause super plastic behavior of metals

Vd

B

B1

Vp

ß

Vp

Cladding Jet

Steel plate

Explosives

Collision point

S

Metallic bond between Al Metallic bond between Al and Feand Fe

Metal bond

Ironatoms

Aluminiumatoms

Electronclouds

Nucleus

Applications in the marine Applications in the marine sectorsector• Cruise vessels and Cruise vessels and

mega yachtsmega yachts

• Offshore platformsOffshore platforms

• Fishing vesselsFishing vessels

• FerriesFerries

• Tenders and supply Tenders and supply boatsboats

• Special ships such as Special ships such as navy vesselsnavy vessels

Vacuum cladding

Some examplesSome examples

Differences with open air Differences with open air claddingcladding

• Triplate is manufactured in a Triplate is manufactured in a vacuum environmentvacuum environment

• Therefore we need less explosivesTherefore we need less explosives• This will lead to a smooth interfaceThis will lead to a smooth interface• The result is no oxide The result is no oxide

conglomerations in the interfaceconglomerations in the interface• Better bending properties Better bending properties • Less risk of corrosionLess risk of corrosion• Easy to machineEasy to machine

Three different interfacesThree different interfaces

Smooth wave interface

Undulating wave interface

Turbulent wave interface

Oxide concentrations are visible

Open air cladding versus Open air cladding versus vacuumvacuum

Open air cladding

Source: http://www.fme-cwm.nl/Download/Publicaties/vm_115.pdf

Vacuum cladding

Oxide conglomerations are visible

Small holes will initiate corrosion in due course especially when bend

Disadvantage during bending and cutting

Limited fatigue strength

Atmospheric cladded transition Atmospheric cladded transition jointsjoints

Atmosferic clad transition jointsaluminium/steel

Concentrations of oxides are visible

Open air cladding

Side bend testSide bend test

Top: Atmospheric claddedBottom: Vacuum cladded Triplate

Side Bend Test 90°

Open air cladding

Vacuum clad generates no oxide holes

Hammer bend test MIL-J-Hammer bend test MIL-J-24445A24445A

Left: Atmospheric claddedRight: Vacuum cladded Triplate

Oxide holes can initiate cracks after bending

Combination hammer bend and side bend test

The result of crevices The result of crevices

Oxide conglomerations are dangeroussince they could initiate serious corrosionin the interface steel/aluminium. This is a result of an open air cladding.

Result of vacuum cladding. No oxideconglomerations are visible. No creviceor galvanic corrosion.

The strength of the The strength of the interfaceinterface

Even at bending radius 2x width Triplate shows no cracks.

Tensile test

Summary of differencesSummary of differences• Open air claddingOpen air cladding

• Oxides with porosityOxides with porosity

• Oxides initiate fracturesOxides initiate fractures

• Holes initiate corrosionHoles initiate corrosion

• Side bend radius 10x Side bend radius 10x width of the stripwidth of the strip

• Variable weather Variable weather conditionsconditions

• Harder to machine Harder to machine (sawing and bending)(sawing and bending)

• Vacuum claddingVacuum cladding

• 100% dense100% dense

• Does not applyDoes not apply

• Does not applyDoes not apply

• Side bend radius 5x width Side bend radius 5x width or even lessor even less

• Does not apply since it is Does not apply since it is insideinside

• Easy sawing and forming Easy sawing and forming thanks to high ductility thanks to high ductility

The right set-up of TriplateThe right set-up of Triplate

Steel plate

Triplate transition joint

Steel plate

Aluminium superstructure

Acceptable set upGood set upSteel plate

Optimum set up

Transit zone shear strength in Transit zone shear strength in N/mmN/mm22

Relationship between temperature and shear strength aluminium/steel transition joints after 200 hours heat input.

110

96

83

69

55

41

28

14

0 40 90 100 200 260 315 370 425

Temperature °C

Temperature gradient during Temperature gradient during weldingwelding

240°C 670°C

1550°C

Aluminium

Steel

Al/Mg

Temperature

Subjected to normal circumstances. It’s relevant to first weld the aluminium plate to the transition joint

Unacceptable configurationsUnacceptable configurations

Unacceptable set up

Steel plate

Worst possible set up

The interface will overheat during welding. That will cause an hard brittle interlayer.

What happens when the What happens when the temperature is too high during temperature is too high during processing of Triplate?processing of Triplate?

Brittle aluminium iron crystals 760Hv

Aluminium 99,5% 23Hv

Steel 127Hv V= 500x

6,5x

Torque = F x a

aF

F

FF

F

F

Ideal situationTensile strenght min. 275 Mpa100%

Tensile strength min. 205 Mpa75%

Tensile strength min. 165 Mpa60%

Sensitive location for notch effects

Steel plate

1

2

3

Width transition joint must be fourtimes the thickness of thealuminium plate.

Aluminium plate

Tensile test asymmetric set-Tensile test asymmetric set-upup

Triplate is not the weakest link in the chain

Special shapes by means of Special shapes by means of water cuttingwater cutting

Full freedom of design and digitally controlled

Triplate butt weldsTriplate butt welds

• Butt welds are labour intensiveButt welds are labour intensive

• Butt welds are expensiveButt welds are expensive

• Difficult to seal it in a right wayDifficult to seal it in a right way

• Avoid butt welds as much as possibleAvoid butt welds as much as possible

• Therefore longer lengths available (5.8 Therefore longer lengths available (5.8 m)m)

Various approvals such as Lloyd’s, Various approvals such as Lloyd’s, Veritas, RINA, Germanische Lloyd, Det Veritas, RINA, Germanische Lloyd, Det Norske Veritas and American Bureau Norske Veritas and American Bureau of Shippingof Shipping

Many thanks for your Many thanks for your attentionattention

www.krontech.no